Lesson 7: Publishing XRD Results - Rietveld refinementprofex.doebelin.org/.../2014/02/Lesson-7-Publishing-XRD-Results.pdf · Lesson 7 Publishing XRD Results ... Match the level of

Lesson 7Publishing XRD Results

Nicola Döbelin(‘s humble opinions…)

RMS Foundation, Bettlach, Switzerland

October 16 – 17, 2013, Uppsala, Sweden

…totally irrelevant to the rest of the world

Relevant Topics

2

- Accuracy of Rietveld refinement results

- Graphs

- «Experimental» section

Accuracy of Rietveld Refined Data

3

Standard procedure:

- Do multiple measurements

- Calculate mean and standard deviation

How good is your analysis?

Is there a systematic error / bias? Caused by:

- Your instrument configuration

- Your sample preparation

- Your refinement strategy

Much trickier question:


4

- Often no complementary analyticaltechnique available

- Hardly any reference materials available

- Refinement: Highly operator dependent

XRD / Rietveld refinements are very difficult to validate:

One option: Participate in round robins

� Compare your results with other labs

Round robin on CaP phase quantificationorganized by RMS Foundation / Nicola Döbelin


5

Round Robin (unpublished):

- Simple 2 phase system: HA + β-TCP

- Very homogeneous distribution

- No texture

- No micro-absorption

- Highly crystalline

- Mean cryst size ~200 nm

0.01 0.1 1 10 1000

2

4

6

8

10

Qua

ntity

[%]

Particle Diameter [µm]

Volume Number

0.01 0.1 1 10 1000

2

4

6

8

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Qua

ntity

[%]

Particle Diameter [µm]

Volume Number

� Nearly «Best Case» Scenario


6

5 Samples measured on Bruker D8 at Ångström Lab

Sample β-TCP [wt-%] HA [wt-%]

1 28.44 71.56

2 28.72 71.28

3 28.90 71.10

4 28.70 71.30

5 28.62 71.38

Mean (Std. Dev) 28.68 (0.17) 71.32 (0.17)

Round Robin

10 Labs with 21 different instruments / configurationsanalyzed the same powder

27.0

27.5

28.0

28.5

29.0

29.5

30.0

b-T

CP

[rel

. wt-

%]

27.0

27.5

28.0

28.5

29.0

29.5

30.0

b-T

CP

[rel

. wt-

%]

27.0

27.5

28.0

28.5

29.0

29.5

30.0

111 3

JJIHHGCBAAA

b-T

CP

[rel

. wt-

%]

A B C DLab E F G H I J

Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2

27.0

27.5

28.0

28.5

29.0

29.5

30.0

111 3

JJIHHGCBAAA

b-T

CP

[rel

. wt-

%]


Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2

27.0

27.5

28.0

28.5

29.0

29.5

30.0

111 3

JJIHHGCBAAA

b-T

CP

[rel

. wt-

%]


Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2

27.0

27.5

28.0

28.5

29.0

29.5

30.0

111 3

JJIHHGCBAAA

b-T

CP

[rel

. wt-

%]


Instrument 1 2 31 2 1 2 1 2 1 2 1 2 1 2 1 2


7

D8 Ångströmlabn=5

28.68 (±0.17) %

Meann=105

28.17 (±0.53) %

p < 0.01


8

Results for this scenario* (Round Robin 2-phase sample):

* only for this scenario!

Repeatability:

- Same Lab

- Same Instrument

- Same Configuration

- Same Operator

- Same Refinement Software

- Same Refinement Strategy

� σQuantification = 0.21 wt-%

Reproducibility:

- Different Lab

- Different Instrument

- Different Configuration

- Different Operator

- Different Refinement Software

- Different Refinement Strategy

� σQuantification = 0.53 wt-%

σ will increase for more complex samples


9

[1] Doebelin, N. «Round robin on calcium phosphate phase quantification by powder diffraction», in preparation.

[2] Stutzman, P. «Powder diffraction analysis of hydraulic cements: ASTM Rietveld round-robin results on precision.» Powder Diffraction, 2005, 20(2): 97-100.

Sr = Reproduced Standard Deviation (different lab / instrument / config / operator / software / refinement strategy)

sr = Repeated Standard Deviation (same lab / instrument / config / operator / software / refinement strategy)

The round robin has demonstrated:

- Small standard deviation ≠ accurate results

- Most labs obtain biased results(from insignificant to highly significant bias)

- Rule of thumb: [1] and [2] show that for phase quantificationsSr ≈ 2 · sr

In a nut shell:


10

General consensus in the Rietveld Community:For n=1: Forget about the decimals!

Publish as:

HA: 100 wt-%

betaTCP: not detected

- Do multiple measurements and report Std. Dev. σ(ignore bias)

- Do multiple measurements and report [1]:Repeatability R = 2.77 · sr(more realistic error bars)

- Do a full test validation to calculate accurate and realistic σ(extremely difficult and time consuming)

3 options to report refined phase quantities in publications:

Probably themost feasibleProbably themost feasibleProbably themost feasible

[1] ASTM E177-13: «Standard Practice for Use of theTerms Precision and Bias in ASTM Test Methods».

10 15 20 25 30 35 40 45 50 55

Inte

nsity

(a.

u.)

Diffraction Angle (°2θ)

10 15 20 25 30 35 40 45 50 55

Inte

nsity

(a.

u.)


Methods… phase quantities

were calculatedfrom XRD data…

Graphs: XRD / Rietveld are «visual» methods

11

Is the data

good

enough?

Your friendly reviewer


12

Methods… XRD data was

analyzed byRietveld

refinement…

How good

was the

refinement?

10 20 30 40 50 60-1000

-500

0

500

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2000 Iobs Icalc Idiff Background

Inte

nsity

[cou

nts]

Angle [°2theta]

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Iobs Icalc Idiff Background

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nsity

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nts]

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nts]

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nts]

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ty [

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nts]

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Recommendation:

- Show all your raw data(documents your data quality)

- Show 1 full refinement(documents your refinement quality)

- All the information is in the raw data

- Only additional information in refinement plots (Icalc, Idiff, Bkgr):

«The refinement was done right»


14

10 15 20 25 30 35 40 45 50 55

25 °C

1000 °C

950 °C

900 °C

850 °C

800 °C

750 °C

700 °C

650 °C

600 °C

550 °C

525 °C

575 °C

25 °C

Inte

nsity

(a.

u.)


500 °C

HAα-TCPβ-TCP

10 15 20 25 30 35 40 45 50 55

25 °C

1000 °C

950 °C

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850 °C

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525 °C

575 °C

25 °C

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nsity

(a.

u.)


500 °C

HAα-TCPβ-TCP

10 20 30 40 50 60

0

500

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1500


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nsity

[cou

nts]

Angle [°2theta]

10 15 20 25 30 35 40 45 50 55

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Inte

nsi

ty (

a.u.

)


500 °C

HAα-TCPβ-TCP

30 31 32 33 34 35 36

0

500

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1500

Iobs Icalc Idiff Background b-TCP HA

Inte

nsity

[co

unts

]

Angle [°2theta]

Combine your raw patterns

30 31 32 33 34 35 36

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nts]

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Show more graphs if themanuscript improves

«Materials and Methods» Section

15

Used for phase identification

Match the level of detail to the relevance of XRD for the study

- Basic intrument parameters:

- Instrument / Manufacturer

- Scan range (start, end, step size)

- References to PDF / ICDD / COD phaseentries


16

10 20 30 40 50 60

0

500

1000

1500


Inte

nsity

[cou

nts]

Angle [°2theta]


17

Used for phase quantification

- Detailed intrument parameters:

- Instrument / manufacturer

- Scan range (start, end, step size [°2θ])

- Radiation, filter / monochromator, divergence slit

- References to sources of crystal structures

- Rietveld software (program name, version, reference)


18


19

Used for advanced refinements(structural parameters, amorphous fractions, crystallite size analysis, texture analysis etc.)

- Detailed intrument parameters:

- Instrument / manufacturer

- Scan range (start, end, step size [°2θ])

- Radiation, filter / monochromator, divergence slit

- … (detector, masks, ASS, Soller slits, generator sett ings…)

- References to sources of crystal structures

- Rietveld software (program name, version, reference)

- Refinement strategy

- Any non-standard calculations, sample preparations, measurement conditions, etc…


20

Refinement strategy


21

Special calculations

Summary: DOs and DON’Ts in Manuscripts

22

Do:

- Show your raw data (stacked plots)

- Show one full refinement

- Give details according to the relevanceof XRD data for the manuscript

Don’t:

- Spam the manuscript with refinement plots

- Publish results from non-standard samples

- Publish results from poor refinements!!!

23

Thank you !

Lesson 7: Publishing XRD Results - Rietveld refinementprofex.doebelin.org/.../2014/02/Lesson-7-Publishing-XRD-Results.pdf · Lesson 7 Publishing XRD Results ... Match the level of

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